Automatic switch for use in telephone or like systems



I Nov.v 11; 19 41. I C.,E,.BEALE1 ETAL 2,262,446

AUTOMATIC SWITCH FOR USE IN TELEPHONE OR LIKE SYSTEMS Filed Dec. 20', 1937 2 Sheets-Sheet 1 FROM LINE 3 FIN DER LP 12 on IIIIIII- g' /NVENTOR5 CHARLES EDMUND BEALE lDP/S TREVOR RICHARDS Nov. 1 1, 1941. c, E, BEALE ETAL 2,262,446

AUTOMATIC SWITCH FOR USE IN TELEPHONE OR LIKE SYSTEMS Filed Dec. 20, 1957 2 Sheets-Sheet 2 OVE'RFLOW 1 M ETER IN VE N TORS CHARLES EDMUND BEAL E $113 V01? RICHARDS ATT.'

Patented Nov. 11 1941 UNITED STATES PATENT- AUTOMATIC swrron Fort USE IN PHONE on LIKE SYSTEMS FFICE TELE- Charles Edmund Beale and Idris Trevor Richards Liverpool, England, assignors to Associated Telephone & Telegraph Company, Chicago, 111.,

a corporation of Delaware Application December 20, 1937,Serial In Great Britain January 11, 1937 Claims. (01. 179-18) The present invention relates to automatic switches for use in telephone or like systems and particularly electromagnetically-operated step-by-step switches of the two-directional type arranged to have all their movements controlled bytwo operating magnets only.

Switches of this type and particularly vertical and rotary switches havegenerally been arranged to have so-called rectangularmotion, that is to say releas is effected by theaclvancement of the Wipers beyond the end of the bank contacts after which they fall and. are then rotated back to normal under the bank by spring tension. Such a movement may not always be sufiiciently rapid where the switch is required to absorb a digit and in such cases itis possible to provide speedier release by arranging for the wipers to return along the path over which they were set. In the case of digit absorption however the wipers will of the primary magnet, the circuit arrange .ments of the magnet are such that in all circumstances the switch wipers are restored to normal by the re-operation of the primary magnet.

According to another feature of the invention in a two-directional electromagnetically operated step-by-stepautomatic switch provided with only .two operating magnets and adapted to have its wipers restored to normal along thepa'th over which they were set in response to re-operation ofthe primary magnet, the circuit arrangements of the magnet are such that in all circumstances after the switch has been seized for use the primary and secondary magnets are operated in turn and theprimary magnet is again operated before the switch is renderedavailable for 'furtheruse. Still another feature of the invention is that in a two-directional electromagnetically operated step-by-step automatic switch provided with only two operating magnets andadapted to have its wipers restored to normalalong the path over which they were set in response to re-operation of the primary magnet, after a connection has been extended overthe switch wipers, a circuit is completed for the primary magnet which thereupon operates to restore them to normal.

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawings comprising Figs. 1 and 2. These when arranged side by side form a circuit diagram of a so-called digit-absorbing group selector of the vertical and rotary type which has access to one or other of two sets of outlets. After theswitch has beenstepped vertically to a particular level, it is caused to releasethereby absorbing the first digit while at the same time the outgoing leads are changed over to a second set of wipers. In response to the second digit the switch again steps vertically and then hunts automatically in the rotary direction for a free outlet? in the appropriate group of the secondset. If the wipers are operated by the first setting digit to any other level the switch functions as an ordinary group selector and hunts for a free outlet in the appropriate group of the first set.

leads by induction from the Underall release conditions the wipers are restored to normal along the path over which they were set. i

Considering now the circuit operation, when the calling partys loop isextended across the incoming negative and positive conductors, relay A operates over its outer windings in series and at armature al operates relay B which looks over armature b2. A guard earth is thereupon applied to the incoming P conductor by way of armature bl whilst relay ON is operated by way of its lower winding over armature b3. Relay ON upon operating energises relay C over its lower windingby way of armature onZ, contacts NR3, armature b5 and resistance YC to battery,

completes a'holding circuit for relay A at armatures on3 and 011.4 independently of armatures c2 and c3 and at armature on5 completes a circuit to light the supervisory lamp LP which is connected to battery over common conductor I2 byway of equipment which is arranged to give an alarm if the switch fails to step off-normal and operate relay H within a predetermined period. Assuming that the switch is functioning as a first selector, the middle winding of relay A is now connected at armature 0028 to an earthed dial ton transformer over common lead ll, so that dial tone is applied to the incoming speaking middle winding of relay A to the two outer windings in order to inform the calling party that he may commence to dial. Relay C at armature c5 prepares the impulsing circuit for the vertical magnet VM, the magnet however being non-operative in series with relay B, while at armature c6 relay C completes a locking circuit for itself which is independent of the vertical magnet interrupter contacts cm.

On reception of the first train of impulses, relay A responds and each time it releases a circuit is completed to energise the magnet VM as follows: earth, armatures M, M and ml, the low resistance upper winding of relay C in parallel with a spark quench resistance YA, armature c5, magnet VM to battery and accordingly the switch wipers are raised to the level corresponding to the digit dialled. During the impulse train relay B is intermittently short-circuited at armature al but this relay. remains operated due to the slugging effect of the shortcircuiting. The presence of metal rectifier MBA in the energising circuit of relay B prevents the slowing down of the magnet operation which would otherwise result by the direct connection of a comparatively low value non-inductive resistance YB in parallel with its winding. It will be readily understood that neither the vertical magnet nor relay C will hold operated in series with relay B and moreover the inductance of the latter relay is such that it has no, appreciable effect on the magnet performance.

On the first vertical step the off-normal springs are mechanically operated and at contacts Nl relay H is operated by way of its middle winding in a circuit including armature 06, contacts NPI, NRI and NI, armature onl and contacts NR2. Relay H thereupon at armature hi connects its right-hand winding to the test wiper Pl at armature 7L5 short-circuits the lower energizing winding of relay C so that the slugging effect thus produced enables relay C to hold operated during the train of impulses which intermittently energise its upper winding and at armature 'h4 disconnects the lamp LP and completes alocking circuit for relay ON over its lower winding.

Assuming first that the wipers have been raised to an ordinary level, that is, a level not set aside for digit absorption, the normal post springs NP will not be operated and the switch will function as an ordinary group selector.

Atthe end of the impulse train, relay A remains steadily operated and maintains relay B while after a short interval relay C releases and completes an energising circuit for the rotary magnet RM as follows: earth by way. of delayed alarmequipment on to the common lead l0, test jack springs T2, armature 011.6, rotary magnet interrupter contacts rm, armatures ht and c4, magnet RM to battery. The wipers are thereupon advanced into engagement with the first set of contacts in the level selected and the rotary magnet interrupter contacts are opened. The rotary elf-normal springs are operated on the first'rotary stepand at contacts NR1 the operation of relay ON-is made dependent on armature h'4 while during the transit time of contacts NR2 relay H remains held byway of its left-hand winding in parallel with the magnet RM'before the contacts rm open.

If the test wiper Pl encounters an engaged outlet, which is indicated by the presence of earth or booster battery potential, relay H-will be held operated over its. right-hand winding by way of armature hi, 11th step cam contacts S2, armature do l and the wiper PI and the disconnection pf'itsforiginal' holding circuit over its lef-t-hand the Pl wiper.

and middle windings by the interrupter contacts Mn is therefore without effect. The rotary magnet de-energises however and on the closure of its interrupter contacts the magnet is re-energised to advance the wipers to the second set of contacts in the level selected. This stepping operation continues automatically until an idle outlet in the group is reached, or alternatively the wipers are advanced to the 11th position.

.If the Pl wiper encounters a free outlet, that is, .one unmarked by earth or booster battery potential, relay H will quickly restore and at armature hi6 further .opens the magnet driving circuit whilst the selected outlet is immediately busied from earthover armatures M, M and dad and The holding circuit for relay ON is now disconnected at armature M and this relay releases whereupon relay C is re-operated in the circuit: earth, interrupter contacts vm, normal post contacts NPI, lower winding of relay C, armature on2, rotary off-normal contacts NR3, armature b5, resistance YC to battery. Relay C thereupon at armatures c2 and c3 disconnects relay A and switches the incoming speaking leads by way of armatures daZ and (M3 to the first set of negative and positive wipers. Relay A upon releasing at armature al short-circuits relay --B and during the release time of the latter relay, relay H is re-operated from earth, armatures 122, all, on! and 04, contacts NR2, middle winding of relay H to battery. Meanwhile the loop extended over the negative and positive wipers operates the A and B relays in the succeeding selector, whereupon a guard earth is returned over the P lead to maintain relay H by way, of its right-hand winding when relay B releases after its slow period.

In response to the dialling of the second and subsequent digits, trains of impulses are transmitted over the first set of negative and positive leads tosucceeding switches to route the call to the wanted party.

If all outlets in the level selected prove busy, the wipers are rotated to the 11th position where the cam springs are mechanically operatedand at-contacts S2 the holding circuit for relay H over its right-hand winding is disconnected. Relay H now releases as described previously, opens-the magnet driving circuit, releases relay ON and reoperates relay C. Armatures c2 and c3 thereupon switch the incoming leads as before-through to the negative and positive wipers, which however now'connect by way of the multipliedllth step contacts back again to the outer windings of relay A which therefore remains held over the incoming-loop and maintains relay B. Cam contacts SI connect up the busy tone transformer over common lead l-3to the middle winding of relay A whereupon busy toneis induced in the outer windings and is appliedin a balanced circuitto the incoming speaking leads.v

Cain contacts S2 extend earth from armature blover armature da4 tothetest wiper Pl to operate anoverflow meter which may be connected to thellth outlet of that particular, level for traffic observation purposes.

-Considering now the case in which the'first digit dialled raises the switch wipers to .a level on which discrimination takes place, the normal post springs are mechanically operatedgby the switch shaft when this level is reached. On release of relay '0' in the normal manner, an energising circuit for the rotary. magnet RM is completedat armature 04 as beforeand as .a result the Wipers are advanced into enga ementwith the first outto leave the P contactassociated with this particular set disconnected in order to cause the switchto be, released by wayof the path over which it was set. On this level therefore, since the Pl wiper encountersnopotential, relayH releases in the usual manner and at armature h6 disconnects the magnet energising circuit, while at armature h4relay0N.is released. Owingto theopening of contactsNPl. relayC is not operated in this "case and moreover a circuit is completed for the vertical magnetfrom earth, armature d115, normal post contacts -NP2, armatures b4 and k3, off normal contacts N2, armature c5, verticalmagnet to battery. The vertical magnet pawl when operated is arranged to engage with an "eirtension'arm of the-rotary detent and move it outof engagement-with the rotary ratchet member so-as to initiate the full release of the switch along the path over which it'has been set, for instance by theuse of a pivoted vertical ratchet memberin the manner described in British Specification No. 399,815, complete accepted Oct. 11, 1933. This arrangement reduces the release time to a minimum and enables the switch to be satisfactorily releasedin an interdigital period. During therelease operation the ver-* tical magnet interrupter contacts cm in the operated position maintain the energising circuit for the vertical magnetindependently of the normal post contacts NPZ which open as soon as the switch commences to restore vertically and these contacts omalso ensure that relay ON isnot reopelated until the switch'has fullyrestored to normal. "When this occurs, all mechanicallyoperated springs are restored to normal condition and hence the 1 opening of the contacts N2 removes the short-circuit frorn the low resistance lower windingof relay DAjand this'relay now operates in series with the vertical magnet which remains held inthis condition. Relay DA at armature d al locks over its upper winding,

at armatures da2,da3 and 'da4 switches over the incoming leads to the second set of wipers, at armature da6 cuts oif the dial tone circuit and at armature da connects earth over contacts NPI and NRI and armature D3 to operate relay ON by way of its lower winding. Relay ON thereupon at armature 0122 completes a circuit for the lower winding of relay C which at armature 05 opens the circuit of the vertical magnet VM and transfers it to the impulsing circuit in preparation for the second train of impulses. l On the dialling of the second digit, the switch steps vertically and then performs an automatic rotary search for a free outlet in the manner previously described but in this case hunting takes place over outlets in a group of the second set of lines. It will be noticed that any further operation of the normal post springs NP is madeineffective at armature da5 and hence any digit may be dialled as the second digit.

on the release of the connection at the conclusion of conversation, earth is removed from the P conductor at the controlling succeeding switch in the train thereby releasing relay H. This relay thereupon at armature k2 opens the holding circuit of relay C and at armature h3 prepares an energising circuit for the vertical magnet VM. This circuit is completed on reon cannot be utilised and it is thereforearranged 3 lease of relay C from earth supplied to common conductor l0, test jack springs T2, armatures bland k3, oil-normal contacts N2, armature c5, magnet VMto battery. Accordingly in the manner previously described the energisation of this magnetinitiates the release of the switch along the path over which it has been set. When theswitch wipers reach the normal position, the off-normal contacts N2 are again opened and disconnect the magnet energising circuit and the switch is then available for further use.

At the commencement of release a momentary unguard period on the incoming P conductor represented by the sum of the release times of relays H and C is provided to enable preceding switches to restore. On the release of relay C followingthat of relay H, earth is applied over off-normal contacts N3 and armature cl to the. incoming P conductor to guard against seizure during. release. When the switch reaches normal, contacts N3 open and remove the guarding earth thus freeing the switch for further use.

Consideration will now be given to the operation in cases where the subscriber hangs up prematurely. If this occurs during dialling, relay A maintains relay C and the vertical magnet during the release time of relay B. On release of relay B after its slow period, this circuit is opened and after a further short interval relay C releases. 'Ihereupon a self-interrupted driving circuit is completed in the normal manner for the rotary magnet .RM from the earthed common conductor [0 and accordingly the wipers are rotated until they encounter a free outlet or alternatively reach the 11th position when relay H releases to cut the driving circuit as previously described. On release of relay H, relay ON is released in turn While the earthed common lead It] is extended over armatures b4 i and M to energise the vertical magnet and bring about the backward release of the switch in the manner previously described. If the calling party should hang up during the hunting movement, the rotary search will continue until a free outlet is encountered when relay H will release and energise the Vertical magnet asbefore to bring about backward release of the switch. Should the subscriber hang up without dialling, the vertical magnet will be energised during the release time of relay B and relays C, ON and i H will also be operated. On release of relay B, relay C and the magnet VM are de-energised and I ,on release of relay C a self-driving circuit is completed for the rotary magnet RM and the circuit operation then proceeds as described above.

Should a maintenance officer desire to attend to the switch, he is able to guard it against seizure during this time by short-circuiting the test jack springs Tl by means of a suitable link provided for the purpose, whilst the removal of the link from the test jack springs T2 enables him to manually step the switch vertically and rotate it as desired, After the inspection or adjustment is completed, the switch maybe restored to normal by the re-insertion of the link into springs T2 and then freed for further use by removal of the link from springs Tl. If the switch has only been stepped vertically, the closure of the off-normal contacts NI brings about of its upper winding and this relay in turn energises relay H over its middlewinding. Hence on the re-insen tion of the link into the springs T2, 9. self-interrupted driving circuit is completed for the rotary magnet from the earthed lead I!) and release subsequently takes place in the manner just described. If the switch wipers have been rotated into the bank, on re-insertion of the release link since relays ON and H are already normal (their operating circuits having been broken by the operated rotary off-normal contacts NB!) the vertical magnet VM will be energised immediately to bring about the release.

A test buzzer connected to test jack springs T4 over common lead 14 and armature da'l enables the set of wipers in use to be determined without removing the dust cover from the switch.

We claim:

1. In an automatic switch for extending connections over any of a plurality of lines responsive to the receipt of impulses, wipers,' means adapted to initially move said wipers to give them access to certain of said lines, means adapted to then move said wipers to select one of said certain lines, and means responsive to the seizure of said switch and the subsequent initiation of the release thereof without transmitting .impulses thereto for first operating said first means, then operating said second means and finally reoperating said first means.

2. In a drop back switch, wipers having a normal position, a plurality of groups of lines accessible to said wipers, stepping means for moving said wipers to select a group of lines, a second stepping means for moving said wipers to select a line in the group thereby to enable a connection to be extended over the wipers and that line, means for automatically reoperating said first stepping means to cause the wipers to be restored to their normal position whenever a predetermined group of lines is selected, and means for also reoperating said first stepping means to cause the wipers to be restored to their normal position responsive to the release'of a connection extended over said wipers.

3. In a switch wherein wipers which have a normal position and which are moved therefrom responsive to impulses comprising a first digit sometimes extend a connection over a line of the group designated by that digit and at. other times are restored to their normal position to be moved therefrom responsive to additional impulses comprising a second digit to extend a connection over a line of the group designated by the second digit, impulse operated means ,for moving said Wipers to give them access to the lines of a particular group, means for then moving said wipers into association with aline of that group, means for at times initiating the restoration of the wipers after said first digit, and means for initiating the restoration of the wipers responsive to the release of a completed connection, said last two means effective to reoperate said impulse operated means to cause the wipers to be restored. Y

4. In a switch having two wiper sets and wherein responsive to the receipt; of impulses comprising a certain digit a connection is extended over one wiper set and a line of the group designated by that digit and responsive to the receipt of impulses comprising a difierent digit followed by impulses comprising a second digit a connection is extended over the other Wiper set and a line of the group designated by the second digit, impulse operated means for moving the wipers from their normal position to give them access to the lines of a particular group, means .for moving the wipers into association with a line of that group, means for extending a connection over the wipers and that line, and means responsive to the release of the connection for reoperating said impulse operated means to cause the wipers to be restored to their normal position.

5. In a switch as claimed in claim 4, wherein the wipers are moved from their normal position responsive to impulses comprising either said certain digit or said other digit, means effective responsive to the receipt of impulses comprising only said certain digit for reoperating said impulse operated means to cause the Wipers to be restored to their normal position.

' CHARLES EDMUND BEALE. IDRIS TREVOR RICHARDS. 

